Thursday, June 12, 2008

Tune-Deaf People May Hear a Sour Note Unconsciously

From NIH
Tune deafness [occurs] in an otherwise normal, uninjured brain,” said James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. “[THis may make it possible to use] tune deafness … to study consciousness.”

A person who is tune deaf is unable to perceive pitch, reproduce melodies, or identify deviations in a melody. According to geneticist Dennis Drayna, Ph.D., one of the study authors, not only is music not enjoyable for people with tune deafness, many of them don’t fully understand what music is. “For severely affected tune-deaf people, Yankee Doodle is no different than traffic noise in Manhattan. It’s fairly meaningless to them,” he said."

Volunteers [half tune deaf and half controls] listened to 102 familiar melodies, roughly half of which were correct, and half of which contained [an] errant last note. The researchers then sifted through the EEG data to isolate the brain’s response to a specific stimulus—in this case, the right or wrong note.

Of principal interest were two signals that brains normally generate when they are presented with a stimulus that doesn’t match what the brain expects to hear, such as the wrong note in a song. The first, the mismatch negativity (MMN), is a large negative signal that occurs roughly 200 milliseconds after the unexpected stimulus is heard; the second signal, the P300, is a large positive signal occurring roughly 300 milliseconds after the unexpected stimulus.

Because tune-deaf people consistently don’t recognize when a wrong note is played or sung, the researchers hypothesized that their brains would not generate the MMN or P300 signals, and as expected, this was true for the MMN signal. However, in the case of the P300 signal, tune-deaf volunteers were processing the wrong note in the same way as the normal participants, even though they weren’t consciously aware of the deviation. [emphasis added] Other brain signals demonstrated that correct notes were being processed equally well for both tune-deaf and normal volunteers.
I didn't know there were brain signals for unexpected stimuli.

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